1. Field of the Invention
The present invention relates to sharing routing information in a link state routing protocol.
2. Description of the Related Art
Networks of general purpose computer systems and specialized devices connected by external communication links are well known and widely used in commerce. The networks often include one or more network devices that facilitate the passage of information between the computer systems and devices. A network node is a network device or computer or specialized device connected by the communication links. An end node is a node that is configured to originate or terminate communications over the network. An intermediate network node facilitates the passage of data between end nodes.
A link-state protocol floods routing information to all intermediate network nodes on a sub-network in a link-state protocol control plane data packet. Each node sends only the portion of the routing information that describes the state of its own links. Link-state data indicates direct links between an intermediate network node that performs routing functions (a router) and a different neighboring router (a router on the same network segment, which does not involve an intervening third router). The link-state data also indicates other characteristics of those links, such as bandwidth and congestion. According to link-state methods, each router builds a model of the entire network based on the link-state data received from other routers in the same.
In some network designs, it is desirable to configure edge routers connected to end nodes so that other routers in the network will not use the edge router as a next hop towards any destination other than those end nodes. An edge router so configured is called a non-transit router or a stub router. Configuring a stub router has been accomplished using a distance vector protocol, which summarizes routing information before passing such information along to a neighboring router. Example distance vector protocols include the routing information protocol (RIP) and the enhanced interior gateway routing protocol (EIGRP) of CISCO SYSTEMS, INC,™ of San Jose Calif.
However, techniques used in distance vector protocols do not work when using a link state protocol, because each node in a link state protocol builds its own model of the entire sub-network that uses the link state protocol. Furthermore, modifications to the link state protocol used on all other routers in the sub-network is not desirable because there are a large number of such routers already deployed.